The present invention relates generally to air brake systems and more specifically for an air brake system and a relay valve to be used in a vehicle convertible between highway and railroad modes of use.
There has always been a great interest in the combined transportation of highway and rail vehicles. This has generally included the loading of road trailers onto flat bed rail cars which are then transported across the rails and then driven to location away from the rails. Efforts have also been made to equip trailers with road wheel and rail wheels such that the trailer itself forms both a road trailer and a rail car. One such vehicle is described in U.S. Pat. Nos. 4,202,276 and 4,202,277 to Browne et al. The major problem with the prior art system, including that of the above-mentioned patents, is that the designers have generally designed a brake system using highway technology and criteria which is unacceptable for use in a rail system.
As an example, the system in the aforementioned patents use a straight air brake system to operate the brake. In this system the pressure and the brake pipe line are used to control a relay valve which in turn controls the brakes. This style of system had been used extensively in rail vehicles but has been replaced by ABD (air brake diaphragm) valves wherein the valve is responsive to modulation of the brake pipe pressure to produce its own brake control signal. A major advantage of the ABD valves is that they provide better control and quicker response as well as the capability of providing braking control for longer length train.
In response to the need for a brake system for a vehicle which is capable of highway and railroad operation with a rail fluid brake system meeting the standards of the rail industry, New York Air Brake Company, a unit of General Signal, developed the brake system illustrated in FIG. 1. Basically it consists of a manifold 28 with a plurality of off-the-shelf elements to operate as a relay valve in combination with an ABDW valve 22 to control the brake cylinder 14. The specific elements and their operation will be described below. Simultaneously with the construction and testing of the manifold relay valve of FIG. 1, New York Air Brake Co. developed the relay assembly in my U.S. Pat. No. 4,421,360. This assembly incorporated the valve functions in a common housing, provided a true variable load proportioning valve as well as other unique features. This system is illustrated in FIG. 2.
The industry has determined that there is a need for a brake system for a vehicle which is capable of highway and railroad operation in between the manifold system of FIG. 1 and the sophisticated relay valve system of FIG. 2.
Thus it is an object of the invention to provide a fluid brake control system for a vehicle which may be used for highway as well a rail travel having capability between the manifold relay valve system of FIG. 1 and the sophisticated relay valve system of FIG. 2.
Still another object of the present invention is to provide a relay valve which performs the function of the two above-described prior art relay valves with fewer parts.
A still even further object of the present invention is to provide a single brake cylinder pressure limiting valve which has two different characteristics, one for service brake application and a second for emergency brake applications.
These and other objects are achieved by providing within a single housing, a brake cylinder relay valve with combined highway override, a dual pressure brake cylinder limiting valve responsive to load, highway supply line and rail supply line charge check valves and a rail reservoir protection valve. This is a substantial reduction in the number of valves of the manifold embodiment of FIG. 1 and is even a reduction in the number of valves of FIG. 2.
The brake cylinder relay valve includes a valve spool whose position determines the flow to the brake cylinder, a first piston connected to the valve spool responsive to the control signal from a control valve and a second piston connected to the spool and responsive to the highway supply line to connect the brake cylinder to exhaust. The first and second pistons are coaxial and work in opposite directions to position the spool. The second piston is connected to the spool via the first piston which is allowed to move freely relative to the second piston in the absence of a highway supply line signal and is drivingly connected in response to a highway supply line signal.
The dual pressure brake cylinder limiting valve limits the brake cylinder pressure in response to the load for a service brake signal within a first set of limits and for an emergency brake signal between a second set of limits which are higher than the first set. The limiting valve includes a first piston responsive to load signals to define the first set of limits and a second piston in tandem with the first piston responsive to load signals and an emergency brake signal in the brake pipe for increasing the response of the first piston to the load signals in response to an emergency signal on the brake pipe.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.